Two-tiered Instant Messaging Architecture

A two-tiered architecture splits the Instant Messaging server deployment
into two layers: an access layer and a data layer. In a simplified two-tiered deployment, you might add
one or more multiplexors and servers to the access layer. The multiplexor acts as a proxy for users, and relays
messages to the Instant Messaging server. The data layer holds the Instant
Messaging server database and Directory servers. Figure 20–1 shows a simplified two-tiered Instant Messaging architecture.